A revelation in human terms of the work of the Merchant Navy and the Royal Canadian Navy in the crucial battle of the Atlantic. In port, while their ships are reloaded, sailors of every nationality throng entertainment centres. Ashore, civilians labour to produce munitions and foodstuffs, or learn in training schools to take their place in the Atlantic front line. When once more the ships are ready, minesweepers clear the channel, planes of the air patrol keep watch for distant danger, and another convoy steams out to sea.